1. Field of the Invention
The present invention relates to a safety belt reel-in mechanism having a tensioning arrangement, comprising a piston which is acted upon by pressure medium and which is disposed at a distance relative to the belt reeling-in shaft of the belt reel-in mechanism, and which in the event of triggering can be connected via a cable drive with the belt reeling-in shaft.
2. Description of the Prior Art
A tensioning device which is to be provided on a safety belt reel-in mechanism is disclosed in German Offenlegungsschrift 30 40 667. In this arrangement, a cylinder is mounted on the housing of the belt reel-in mechanism; a piston which is operated by pressurized gas, is movably disposed in the cylinder. By means of a cable drive, the piston is drivingly connected with the reeling-in shaft of the safety belt reel-in mechanism, with the drive cable being permanently connected and, via a cable guide disposed on the piston, being guided within a sleeve placed over the belt reeling-in shaft of the reel-in mechanism. Within the sleeve, the cable is wound several times about the belt reeling-in shaft, from where it extends to a delivery spool. In this arrangement, the turns or windings of the drive cable preferably rest against the inside of the sleeve, and the drive cable should be wound two and a half times about the belt reeling-in shaft.
In the event of an accident, when the pyrotechnical charge disposed in the cylinder is ignited by a sensor associated with the vehicle, and the resulting pressurized gases act upon the piston, the latter, along with the guide roller, is forced in the direction away from the belt reel-in mechanism. As a result, the drive cable is pulled tight, and its windings are held firmly in place in the annular space about an appropriate extension of the belt reeling-in shaft, as a result of which, due to the frictional connection brought about by the wraparound angle, the shaft is turned and thus tightens the safety belt.
However, such a construction of a belt reel-in mechanism having a tensioning arrangement has the drawback that after the pyrotechnical charge is triggered, and after the resulting actuation of the cable drive, a non-releasable coupling of the tensioning arrangement and the belt reeling-in shaft is effected. The result is that after termination of the tensioning or tightening process, the belt reeling-in shaft is locked in its then achieved position and, without removing the tensioning arrangement from the shaft, which can only be effected by appropriate construction of the unit, is no longer able to function in the sense of locking in response to a sensor which is associated with the belt strand and/or the vehicle. Such a locking is described in connection with a belt reel-in mechanism which does not have a tensioning arrangement, for example in conformity with German Offenlegungsschrift 28 23 334.
This inability of the belt reeling-in shaft to function is a serious drawback, because after an unintentional triggering of the tensioning arrangement the self-locking belt reel-in mechanism can thus no longer properly perform its task of securely holding the strapped-in person in place on the seat during an accident, and of preventing forward movement of the body which would otherwise endanger the strapped-in person. If for example a car parked in a garage undergoes an automatic triggering of the tensioning arrangement, this fact cannot be readily determined. However, as soon as a person sits in the vehicle, the belt reel-in mechanism can no longer function for the aforementioned reasons, and thus endangers the safety of the person using the belt in the event of an accident.
An object of the present invention is to further improve a safety belt reel-in mechanism and tensioning arrangement of the aforementioned general type in such a way that even after triggering of the tensioning arrangement, or conclusion of the tensioning process, the belt reel-in mechanism can be reused and can be locked by means of a locking system which is responsive to movements of the belt strand and the vehicle.